Catalytic oxidation of sulfides to sulfoxides using aluminium hydrogen sulfate, sodium nitrite and catalytic amounts of metal bromide

Article abstract of DOI:10.1007/BF03245878

A catalytic, chemoselective and environmentally friendly procedure for the oxidation of sulfides is described. A wide range of aliphatic or aromatic sulfides were successfully oxidized to the corresponding sulfoxides using NaNO₂, Al(HSO₄

Full text of DOI:10.1007/BF03245878

J. Iran. Chem. Soc., Vol. 7, No. 1, March 2010, pp. 190-194.
JOUIRrNaAnLiaOnF THE
Chemical Society
Catalytic Oxidation of Sulfides to Sulfoxides Using Aluminium Hydrogen Sulfate,
Sodium Nitrite and Catalytic Amounts of Metal Bromide
A. Ghorbani-Choghamarani* and J. Zeinivand
Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
(Received 16 January 2009, Accepted 15 March 2009)
A catalytic, chemoselective and environmentally friendly procedure for the oxidation of sulfides is described. A wide range of
aliphatic or aromatic sulfides were successfully oxidized to the corresponding sulfoxides using NaNO2, Al(HSO4)3 and a catalytic
amount of KBr or NaBr in the presence of wet SiO2 (50% w/w) in CH3CN under heterogeneous conditions in moderate to high
yields.
Keywords: Sulfides, Sulfoxides, Homoselectivity, Metal bromide, Heterogeneous
INTRODUCTION
important role as therapeutic agents such as anti-ulcer [8,9],
antibacterial [10], anti-atherosclerotic [11-13] and so on.
In parallel with a good number of reports employing
conventional oxidizing media for this transformation [14-29],
search for new catalysts is still actively pursued to address the
problems like effluent pollution, loss of selectivity and tedious
workup procedures [30]. Sulfoxidation of sulfides by a metal-
free chemoselective oxidation by hydrogen peroxide catalyzed
by the in situ generated dodecyl hydrogen sulfate in the
absence of any organic co-solvent as an environmentally
friendly process is reported [31].
Metal hydrogen sulfates have attracted attention of organic
chemists during the last decade. In addition, the stability and
reasonable prices, heterogeneous nature of the reactions, high
yields of the products, short reaction times, and reusability are
among other important advantages of metal hydrogen sulfates
[1].
Nowadays, most research is focused on the more versatile,
more selective and more reactive catalysts [2]. The
development of efficient and new catalytic systems for various
organic transformations is an active ongoing research area and
the scope for further improvement towards milder reaction
conditions [3].
EXPERIMENTAL
Chemicals were purchased from Fluka, Merck and Aldrich
chemical companies. The oxidation products were
Sulfoxidation reactions are of significant importance in
organic chemistry, medicinal chemistry, and drug metabolism
[4]. Selective oxidation of sulfides to the corresponding
sulfoxides remains a challenge and is interesting because of
the importance of sulfoxides as synthetic intermediates in the
synthesis of biological and medicinal compounds [5-7].
Additionally, some of biologically active sulfoxides play an
1
characterized in comparison with their spectral (IR, H NMR,
and 13C NMR) and physical data with authentic samples.
Oxidation of Dibenzyl Sulfide to Dibenzyl Sulfoxide
(General Procedure)
KBr (0.006 g, 0.05 mmol) was added to a solution of
dibenzyl sulfides (0.214 g, 1 mmol) and wet SiO2 (0.3 g) in
*Corresponding author. E-mail: arashchgh58@yahoo.com

Ghorbani-Choghamarani & Zeinivand
CH3CN (5 ml), followed by addition of Al(HSO4)3 (0.603 g,
Table 1. Oxidation of Benzyl Phenyl Sulfide by Al(HSO4)3,
NaNO2 and Catalytic Amounts of Sodium and
Potassium Iodides and Bromides in the Presence
of Wet SiO2 (50% w/w)a in CH3CN at Room
Temperature
1.1 mmol) and NaNO2 (0.138 g, 2 mmol). The resulting
reaction mixture was stirred at room temperature for 45 min
(the reaction progress was monitored by TLC) and then
filtered. The residue was washed with CH2Cl2 (20 ml). The
filtrates were combined and dried over anhydrous Na2SO4 (1.5
g) which, after filtration and evaporation of the solvent, gave
dibenzyl sulfoxides in 0.216 g, 94% yield; m.p.: 131-134 ºC
(Lit. 132-134 ºC [32]).
Entry
Catalyst
Time (h)
Yield (%)b
c
1
2
3
4
5
5
NaCl
NaBr
NaI
KBr
KI
8
-
25 min
99
c
8
-
RESULTS AND DISCUSSION
30 min
97
c
8
8
-
-
In continuation of our studies on the application of new
oxidizing reagents in the organic transformations [33-38], we
became interested in the use of a novel oxidizing system,
based on the in situ generation of X+, for the selective
oxidation of sulfides to sulfoxides.
c
KCl
aSubstrate/Al(HSO4)3/NaNO2/MX/wet SiO2:1:0.67:2:0.05
(mmol):0.3 g. bIsolated yield. cReaction didn’t complete.
For this purpose, catalytic amounts of sodium or potassium
halides in the presence of Al(HSO4)3/NaNO2 and wet SiO2 in
CH3CN at room temperature was examined. The results are
tabulated in Table 1.
Subsequently, to consider solvent effect, we screened
different solvents for the oxidation of benzyl phenyl sulfide as
model reaction. As it can be seen from Table 2 acetonitrile is
the best solvent in terms of activity and selectivity (Table 2),
therefore all oxidation reactions were performed in
acetonitrile.
With optimized experimental conditions for benzyl phenyl
sulfide in hand, we investigated sulfoxidation reactions with a
variety of aliphatic and aromatic sulfides (Scheme 1 and Table
3).
The catalytic oxidation procedure is very simple and the
products are easily isolated from the reaction media, because
reactions are performed under completely heterogeneous
conditions; therefore products can be easily obtained by
simple filtration and evaporation of solvent.
Table 2. Oxidation of Benzyl Phenyl Sulfide by Al(HSO4)3,
NaNO2 and Catalytic Amounts of KBr in the
Presence of Wet SiO2 (50% w/w) in Different
Solventsa
Entry
Solvent
Time (h)
Yield (%)b
98
1
2
3
4
5
6
7
Acetonitrile
Acetone
Chloroform
Dichloromethane
n-Hexane
30 min
22
20
110 min
23
c
-
d
-
95
c
-
c
Methyl acetate
Ethanol
22
22
-
d
-
aSubstrate/Al(HSO4)3/NaNO2/KBr/wet SiO2:1:0.67:2:0.05
(mmol):0.3 g. Isolated yield. Reaction didn’t complete.
b
c
dNo reaction.
Regarding the role of Al(HSO4)3 in the described system, it
was revealed that sulfoxidation reaction did not perform in the
absence of Al(HSO4)3, which means that the presence of acid
is necessary in this reaction media (Table 3, entry 3). In
addition to aluminum hydrogen sulfate, we examined a variety
of metal hydrogen sulfates in the oxidation of benzyl phenyl
sulfide, as typical example, in the presence of sodium nitrite
and a catalytic amount of NaBr (Table 4). Thus we can apply
different metal hydrogen sulfates instead of Al(HSO4)3 in this
transformation.
Also to show the catalytic role of KBr and NaBr in the
described system, benzyl phenyl sulfide was subjected to the
oxidation reaction without the catalyst. The reaction didn’t
complete within 20 h with the formation of sulfone as a
191

Catalytic Oxidation of Sulfides to Sulfoxides
O
S
byproduct (Table 3, entry 4). By this oxidizing system,
Al(HSO4)3, NaNO2
S
R1
R2
R1
R2
thiantrene was homoselectively oxidized to thianthrene
monosulfoxide (Table 3, entries 19 and 20, Scheme 2). This
result is in almost full agreement with our previously reports
[33-35].
Moreover, to show the chemoselectivity of the described
system, two sulfides containing alcoholic group were
subjected to the sulfoxidation reaction, but alcohol oxidation
did not occur under the mentioned conditions, and primary
hydroxyl groups remained intact during the reaction (Table 3,
entries 13,14, 21 and 22, and Scheme 3).
KBr or NaBr
Wet SiO2
CH3CN, rt
1
2
with R2 =
a
b
c
S
S
Ph
S
d
g
j
e
f
S
S
S
OH
h
i
S
S
OMe
S
A mechanism is also provided for the oxidation of sulfides to
sulfoxides in Scheme 4 based on our previously reported
works [33-35].
O
S
k
S
S
OH
CHO
In summary, we report here an efficient method for the
selective oxidation of sulfides to sulfoxides under completely
Scheme 1
Table 3. Oxidation of Sulfides 1 to the Corresponding Sulfoxides 2 Using Al(HSO4)3 I, NaNO2 II and Catalytic Amounts
of KBr III or NaBr IV in the Presence of Wet SiO2 (50% w/w) in Acetonitrile at Room Temperature
Substrate/Reagent/Catalystsa
Entry
Substrate
Product
Time (min)
Yield (%)b
I
II
2
2
2
2
2
2
2
2
2
2
2
2
3
3
2
2
2
2
2
2
2
2
2
2
III
0.05
--
0.05
--
0.05
--
0.05
--
0.05
--
0.05
--
0.10
--
0.05
--
0.05
--
0.05
--
0.05
--
0.05
--
IV
--
1
1a
1a
1a
1a
1b
1b
1c
1c
1d
1d
1e
1e
1f
2a
2a
2a
2a
2b
2b
2c
2c
2d
2d
2e
2e
2f
0.67
0.67
--
30
25
97
99
--c,d
--d,e
97
95
94
96
96
98
97
91
95
97
98
99
93
82
98
90
93
88
72
98
2
0.05
--
--
--
0.05
--
0.05
--
0.05
--
0.05
--
0.10
--
0.05
--
0.05
--
0.05
--
0.05
--
3
24 h
20 h
300
230
45
4
0.67
0.67
0.67
0.67
0.67
0.67
0.67
0.67
0.67
1.00
1 .00
0.67
0.67
0.67
0.67
0.67
0.67
0.67
0.67
0.67
0.67
5
6
7
8
30
9
55
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
50
25
15
220
205
40
1f
2f
1g
1g
1h
1h
1i
2g
2g
2h
2h
2i
36
25
20
205
220
80
1i
2i
1j
2j
1j
2j
75
1k
1k
2k
2k
60
0.05
45
aSubstrate:wet SiO2 = 1 mmol:0.3 g. bIsolated yield. cWithout Al(HSO4)3. dNo reaction. eWithout KBr and NaBr.
192

Ghorbani-Choghamarani & Zeinivand
Table 4. Oxidation of Benzyl Phenyl Sulfide with Metal Hydrogen Sulfates, NaNO2 and
Catalytic Amounts of NaBr in the Presence of Wet SiO2 (50% w/w) in Acetonitrile
at Room Temperature
a
Entry
M(HSO4)n
mmol of M(HSO4)n
Time (min)
Yield (%)b
1
2
3
4
Zn(HSO4)2
Zr(HSO4)4
NaHSO4
KHSO4
1
0.5
2
35
25
25
99
97
90
95
2
14 h
aSubstrate:NaNO2:KBr:wet SiO2 = 1 mmol:2 mmol:0.05 mmol:0.3 g. bIsolated yield.
O
S
O
S
S
S
Al(HSO4)3, NaNO2
+
KBr or NaBr
Wet SiO2
CH3CN, rt
S
S
O
0%
100 %
Scheme 2
O
S
S
S
Al(HSO4)3, NaNO2
OH
OH
OH
O
+
KBr or NaBr
Wet SiO2
CH3CN, rt
100 %
OH
0%
O
S
S
Al(HSO4)3, NaNO2
S
+
O
KBr or NaBr
Wet SiO2
CH3CN, rt
100 %
0%
Scheme 3
S
R1
R2
NO
Br+
Br
S
Br-
H2O
Al(HSO4)3 + NaNO2
HNO2
O
S
R1
R2
+ 2H+
Scheme 4
193

Catalytic Oxidation of Sulfides to Sulfoxides
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ACKNOWLEDGMENTS
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